An experimental analysis of cancer: role of ras oncogenes in multistep carcinogenesis.

Carcinogen-induced animal tumor models are invaluable resources for studies aimed at understanding the participation of ras oncogenes in multistep carcinogenesis. Mutationally activated ras oncogenes are frequently detected in chemically induced animal tumors. The nature of the mutations in ras oncogenes reflects the chemical specificity of the carcinogen, implying that the carcinogen interacts with ras sequences. In chemically induced rat mammary tumor models, ras activation is the earliest detectable change in the mammary gland cells following administration of the chemical. Further, expression of the tumorigenic phenotype of cells containing activated ras requires the cooperation of normal physiological factors that are active during puberty.